Transcript for Downed Malaysia Airlines Flight MH17: Securing the Site

We're going to start here with disaster, compounded by disrespect. There's no other way to describe what is happening tonight at the mh 17 crash site than chaotic and infuriating. The debris field in eastern Ukraine is being guarded by pro-russian rebels, some of them allegedly drunk, who are restricting the activities of international investigators. The bodies of some of the 2 98 victims, 80 of them kids seen here simply lined up on the side of the road. Tonight the Ukrainian government says it has proof that Russia provided the missile system that shot that plane down and is now actively working with the rebels to cover it all up. We have team coverage tonight and we're going to start with ABC's terry Moran who is on the ground. Terry, good evening. Reporter: Good evening, Dan. We returned from that crash site awhile ago, and I can tell you that as our team left as night was falling, it was completely unsecured with no professional air crash investigators in charge. That scene is compromised and the evidence is evaporating. Today, two days after the crash, the grim task of collecting the bodies of the dead has finally begun. Volunteers digging, bagging and trucking away the victims' remains to be taken to a morgue in the nearby city of donetsk, a separatist rebel stronghold. But so many of the 298 killed are still uncollected from these fields. We arrived late today and were stunned by what we found. Just a few feet off the road one of the wings came down into this field. Frankly, it's outrageous we can get so close. This is evidence completely unsecured. A few locals formed a tiny, lackadaisical perimeter around just a bit of wreckage. Reporters and others tromped around everywhere, the victims' personal items just piled up. Earlier, the international team of monitors claimed some of the rebels supposedly securing the site were "Visibly intoxicated" though we did not see that. So a compromised crime scene, certainly, but there are other places to look for evidence. I think we're going to shift from a mindset of a crime scene investigation to an intelligence investigation to try and figure out how it was that these missiles came to be in rebel hands. Reporter: Ukraine is pointing a finger directly at Russia, claiming they have evidence that the missile they say brought down the plane came from Russia and so did the troops who fired it. We know for sure that the team was Russian. They were Russian citizens operating a buk m1 and they came from the territory of Russian Federation together with the missile launcher. Reporter: And then there's this, that same Russian mobile missile launcher in Ukraine headed yesterday for the Russian border with two of its launch tubes empty. It's a race against time and the chaos of the crime scene to determine what really happened to flight 17. Those quiet fields we visited today have become another battlefield, and the casualty may be truth. Dan? Terry Moran reporting on the chaotic and infuriating scene on the ground in eastern Ukraine. Thank you. Let's bring in ABC news aviation consultant John nance. John, given how thoroughly contaminated this crime scene is now, how badly does that set back the investigation? It sets it back a little bit, Dan, but not as bad as you might think. Here we're not dealing with a mystery of how the plane came out of sky but evidence of what explosive brought it out of the sky, especially when we've got anything that has pitting on it and residue that would be traceable back to a particular type of missile. So that might tell us how the plane came down and what kind of missile was used, but it won't tell us who fired the missile or why. How do we figure that part out? I think that's the question that's going to have to be answered by a lot of basically bringing together of intelligence. Because we know that a lot of tracking is out there from where the missile had to come from. Some of it will possibly be discernible from the wreckage, but I think most of it is going to be from other evidentiary factors. John nance, thank you. This brings us to ABC's Martha Raddatz who is covering the intelligence side of the picture. How does the intelligence community go about finding the perpetrators? One of the things is, this is a conflict zone, so we had all sorts of satellites and radar over that conflict zone and tracked that missile as it left that Ukrainian area, eastern Ukraine, that russian-held area. It basically hit the airplane. We saw the final moments of impact, a fire ball from satellites. What they do is they track it back. They go back, follow the arc backwards to try to figure out where exactly it came from. And that's what you heard the white house say yesterday they believe it came from russian-held territory. That that's how I it was launched. What are the odds that we find the people who did this and then in some way bring them to justice? Well, we've got intercepts, things like that. You saw the pictures that terry Moran showed there. But I think the odds are pretty slim that we'll ever actually find out who pulled the trigger on this. We really want to find out whether there were Russians there, whether there were Russian special forces there helping the Russian separatists. That's a key question and I'm not sure we'll ever know that. If we find out the Russians had any hand in this, even in simply giving the missiles to the rebels, will that change the situation on the ground with this ongoing conflict? That's a good question. Will Putin say this is a bad idea to give them this surface-to-air missiles? It might but in the end, Dan, I think what we have to remember is that this looks like it was an accident. I don't think anyone was actually trying to shoot down a civilian plane. They were trying to shoot down a military plane. An accident and a horrible one at that. Thank you. Martha will be Georgia stephanopoulos on a special edition of "This week" tomorrow morning.

This transcript has been automatically generated and may not be 100% accurate.

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